#include<stdio.h>
double CancelFee(double price);
int main()
{
	double a;
	scanf("%lf",&a);
	double ret = CancelFee(a);
	printf("%.1lf\n",ret);
	return 0;
}
double CancelFee(double price)
{
	double n,m ;
	
	
		m = price * 0.05;
	    n = (int)m;
	    if((m-n)<0.25) {
	    	m = n;
		}
		else if((m-n)>=0.25&&(m-n)<0.75) {
			m =  n + 0.5;
		}
		else if((m-n)>=0.75) {
			m =  n + 1;
		}
	    
	return m;
}
